/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.util;

import java.util.jar.*;

/**
 * A micro-application that prints the main class name out of a jar file. <br>
 * 挺简单的，利用java.util.jar包里面的几个类的几个方法，读取出jar包中的Main-Class属性。PS：擦，这个类谁写的，竟然不是用驼峰命名法
 * ！
 */
public class PrintJarMainClass {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		try {
			JarFile jar_file = new JarFile(args[0]);
			if (jar_file != null) {
				Manifest manifest = jar_file.getManifest();
				if (manifest != null) {
					String value = manifest.getMainAttributes().getValue(
							"Main-Class");
					if (value != null) {
						System.out.println(value.replaceAll("/", "."));
						return;
					}
				}
			}
		} catch (Throwable e) {
			// ignore it
		}
		System.out.println("UNKNOWN");
		System.exit(1);
	}

}
